1. Field of the Invention
The present invention relates to a machining apparatus that performs linear grooving.
2. Description of the Related Art
To machine a diffraction grating or a die for the light guide plate of a liquid crystal display, hundreds to tens of thousands of linear grooves need to be formed. To reduce the time for machining this many linear grooves, a machining apparatus with a high speed feed axis is required. Even minor errors are intolerable in the machining of a diffraction grating or a die for a light guide plate, so a smooth linear motion mechanism that does not generate vibration even when driven at high speed is also necessary. A known feed mechanism that can achieve the necessary high speed and high precision machining has a structure combining an air bearing and a linear motor.
To reciprocate a linear axis at high speed, great thrust force is necessary to reverse its motion. Solutions to this problem were proposed for printers in Japanese Patent Applications Laid-Open No. 5-238093 and No. 2000-94774. In the printers according to these inventions, a shuttle mechanism having a printing head is reciprocated by a linear motor. The linear motor comprises permanent magnets disposed on the printer body and a coil disposed on the shuttle mechanism facing the array of permanent magnets. To reduce the force required by the driving unit at reversal points in the reciprocating motion of the shuttle mechanism, additional permanent magnets are placed at both ends of the array of the permanent magnets. When the reciprocating motion of the shuttle mechanism reverses, an attractive force is generated between the base plate on which the coil is mounted on the shuttle mechanism and the permanent magnets at the ends of the array of permanent magnets, acting to make the shuttle mechanism return to the center of the reciprocating motion. The thrust force required from the linear motor is thereby reduced.
In addition, in a guided continuous reciprocating apparatus that continuously moves or reciprocates an elongate member such as a cable or metal wire, Japanese Patent Application Laid-Open No. 7-137935 proposes a solution in which elastic springs or other objects are placed at both ends of the path of motion of a moving body to store the inertial energy of the moving body and the stored inertial energy is reversed and imparted to the moving body when its motion reverses, so that the driving means that drives the moving body has to produce less thrust force to reverse the motion of the moving body.
A body undergoing reciprocating motion must be strongly accelerated at the points at which its motion reverses. In particular, when the moving body reciprocates at high speed, the high acceleration at the reversal points causes the driving means that drives the moving body to generate a large amount of heat, which affects machining precision. As described above, even small errors are intolerable in the machining of a diffraction grating or a die for a light guide plate, so heat generation from the driving unit needs to be minimized. In addition, if a linear motor is used as the driving unit to obtain high thrust force, thrust ripples and cogging occur, affecting straightness accuracy.